1. Field of Invention
This invention relates generally to electrostatic chucks and their method of manufacture and, in particular, to such chucks that can be manufactured to relatively high standards, for relatively low costs while at the same time eliminating cumbersome manufacturing techniques.
2. Description of the Prior Art
Prior art attempts to accomplish the goals to which this invention is directed, have met with limited success.
U.S. Pat. No. 5,055,964 to Logan, et al discloses a bipolar chuck using an anodized ring insert in an anodized base.
U.S. Pat. No. 5,572,398 to Federlin, et al discloses a tripolar electrostatic chuck using separate positive and negatives electrodes housed on a non-polarized base housing.
The technologies described in U.S. Pat. Nos. 5,055,964 and 5,572,398 are relatively low-cost technologies but suffer the disadvantage that the separate clamping electrodes must be joined to a framed in careful alignment to achieve flatness. The best flatness that can be achieved in manufacturing is about +/-0.00015 inch (+/-3.75 microns) without a final mechanical grinding or lapping step, which causes insulator thickness non-uniformity. Furthermore, U.S. Pat. No. 5,055,964 has inherently unbalanced rf capacitance as well as non-uniform heat transfer for the 2 poles.
In U.S. Pat. No. 5,207,437 to Barnes, et al and U.S. Pat. No. 5,191,506 to Logan, et al, an electrostatic chuck is disclosed including fired ceramic sheets containing metallic layers within, which are then bonded to a metal cooling/heating assembly containing connections to the electrostatic chuck electrodes.
Fired ceramic sheets consisting of conductive layers embedded in a ceramic matrix can be made but must have significant thickness to maintain physical strength and rigidity. This thickness causes the thermal resistance and rf impedance to be much higher compared to sprayed ceramic layers over metal. Cost of these ceramic structures is usually high.
U.S. Pat. No. 5,691,876 to Chen, et al describes an electrostatic chuck with organic coatings, such as polyimide (Kapton) over a metal chuck assembly.
Organic insulators with metal electrodes embedded are commonly bonded to metal frames to make electrostatic chucks. These chucks have good uniform rf coupling and cooling but suffer the disadvantage that they are not robust and are easily attacked by reactive chemicals in a plasma environment and may be easily damaged by physical abrasion.
In U.S. Pat. No. 5,754,391 to Bates crystalline insulator coatings such as sapphire, usually thick sheets, are bonded to the metal chuck surface.
Crystalline insulator coatings such as sapphire have excellent insulating properties but are expensive and difficult to manufacture in thin coatings required for low operating voltage and high thermal conductivity coupling capacitance.
Watanabe, et al U.S. Pat. No. 5,151,846 discloses the fabrication of an electrostatic chuck by pressing a plurality of given ceramic sheets in the form of pastes with electrode films printed thereon, against a ceramic green sheeting serving as a base plate and then firing the laminated body.